* Returns the RSA private key encoded in [PKCS #1][rfc_8017] [PEM format][rfc_7468].
   *
   * [rfc_8017]: https://tools.ietf.org/html/rfc8017
   * [rfc_7468]: https://tools.ietf.org/html/rfc7468
   */
  fun privateKeyPkcs1Pem(): String {
    check(keyPair.private is RSAPrivateKey) { "PKCS1 only supports RSA keys" }
    return buildString {
      append("-----BEGIN RSA PRIVATE KEY-----\n")
      encodeBase64Lines(pkcs1Bytes())

    val keyPair: KeyPair = heldCertificate.keyPair
    val certificatePem: String = heldCertificate.certificatePem()
    val privateKeyPkcs8Pem: String = heldCertificate.privateKeyPkcs8Pem()
    val privateKeyPkcs1Pem: String = heldCertificate.privateKeyPkcs1Pem()
  }

  @Test
  fun heldCertificateBuilder() {
    val keyPair: KeyPair = KeyPairGenerator.getInstance("").genKeyPair()